取代基对2-(2-羟基苯基)苯并噻唑分子内氢键及质子转移的影响:密度泛函理论研究

运用密度泛函(DFT)和含时密度泛函(TD DFT)理论方法研究了在2-(2-羟基苯基)苯并噻唑(HBT)苯环羟基的邻位或对位分别引入羟基和醛基后的衍生物分子内质子转移过程,考察了取代基的电子效应及取代位置对分子内氢键和质子转移反应的影响,模拟计算了各分子的IR振动光谱和电子光谱.研究发现,HBT及其衍生物分子可以形成分子内氢键,且激发态时氢键增强.基态时以醇式构型稳定存在,激发态时酮式结构为优势构象.分子的最大吸收峰和发射峰主要源于电子从前线分子轨道HOMO到LUMO之间的跃迁.基态分子内质子转移需要越过较高的能垒因而难以发生,而激发态时只需越过较低能垒就很容易发生激发态分子内质子转移.取代基的电子效应和取代位置对HBT分子氢键强度、互变异构体的相对稳定性、电子光谱及质子转移反应的能垒均有一定影响.

Subsituent effects on intramolecular hydrogen bond and proton transfer in 2-(2-hydroxyphenyl)benzothiazole: DFT and TD DFT research

The ground state intramolecular proton transfer(GSIPT) and excited state intramolecular proton transfer(ESIPT) reactions of 2-(2-Hydroxyphenyl)benzothiazole(HBT) and its derivatives with electron-donating substituent hydroxyl or electron-withdrawing substituent aldehyde group introduced in meta or para position of hydroxyl in benzene ring have been studied by using density functional theory (DFT) and time-dependent density functional theory(TD DFT) methods, the influence of electronic effects and positions of substituent groups on the intramolecular hydrogen bonds and proton transfer reactions have been explored, the IR vibration spectra and electron spectra of all molecules have been also simulated. The results show that HBT and its derivatives can form intramolecular hydrogen bonds, and which will be obvious enhanced in the excited state. The enol form is the normal form in the ground state, but the keto form is the stable structure in the excited state. The maximum absorption and emission peak of each compound are all mainly ascribed to the transition of electron from frontier molecular orbital HOMO to LUMO. The GSIPT is hard to occur because of the high reaction energy barrier. However, the reaction energy barrier is very low and ESIPT is easy to happen in the excited state for all HBT compounds. In addition, the hydrogen bond strength, relative stability of tautomers, electronic spectra and energy barrier of proton transfer are all affected by the electronic effect of substituent as well as the the substitutional positions with a certain extent.